It must be the same as making a Collection (?) - semantics
I selected everything about the character, then Ctrl g. It asked me if I wanted to make a Collection, so I went along with it. Except this new Collection is not showing in the Outliner with the rest of the collections
It would be nice to know where it is.

Thanks Hadriscus

Update: Well, I don’t know why it would not show in the Outliner, but it did show when I appended it. I found it in the Collection folder

Wait a sec, I’m not too sure we’re on the same page.
I can make a Collection, I know. I think the issue was that when making a collection with the shortcut (Ctrl g), as opposed to using the Outliner, it would not show the collection in the Outliner. But the collection was made nevertheless. I know because after making it I opened the other file and appended the collection I made.
Then when I reopened the file with the collection I was able to see the collection in the Outliner (rolling eyes).
But it’s all good now
Thanks a59303

Yeah collections have to be linked to view layers so in order to see them in the outliner. It makes sense technically because it’s consistent with how datablocks work in Blender, but as most things that make sense technically it doesn’t from a user POV : right now it’s a total hassle to find and link unlinked collections, I can’t even remember how to do it ottomh.